Copper (cubic close-packed) 1: close-packing

To go directly to the unit cell structure, click the link below to page 3.

Copper is unreactive enough to exist uncombined in natural deposits, but these are now all but depleted as economically viable ores. The principal mineral for extracting copper now is chalcopyrite, CuFeS₂. With copper being very malleable, ductile, an excellent electrical conductor and chemically unreactive, it finds great use in electrical wiring and components, and tubing. It forms many alloys, including bronze (with tin), brass (with zinc) and cupronickel (with nickel), which is used for 'silver' coins.

Copper atoms are "close-packed". For a collection of hard spheres, close-packing is the most efficient way of packing them into a lattice. It is easy to show with simple trigonometry that 74% of space is occupied by hard spheres in close-packing. The structure on the left doesn't show hard spheres in contact, even though that approximates what it actually is. Instead the atoms are drawn with half their actual radius. That is because you can't see inside the bulk with a realistic space-filling representation, which is shown on the next page. Also, showing the structure as atoms connected by bonds makes it easier to work out structural characteristics, as bonds are only drawn between atoms that can be considered to be touching. With close packing, the coordination number for an atom in the bulk is maximised. The coordination number of an atom is the number of atoms in contact with it. There are two types of close-packing: "cubic close-packing (CCP)" and "hexagaonal close-packing (HCP)". Copper adopts CCP. Look at the bulk structure of copper to the left and try to see how many nearest, ie touching, neighbours a copper atom in the bulk has.

Go to page 2 to look at the space-filling representation of copper's structure.

Page 2 Page 3 Page 4 Page 5 Page 6